Technical Field
The embodiments herein relate to quantum information science (QIS), and more particularly to QIS used for underwater imaging and navigation.
Description of the Related Art
A major scientific thrust from recent years has been to try to harness quantum phenomena to increase the performance of a wide variety of information processing devices. QIS has emerged as a scientific undertaking that promises to revolutionize our information infrastructure. In particular, QIS offers the possibility of quantum sensors. That is, sensing devices that exploit quantum phenomena in such a way that they perform much better than their classical counterparts. Some examples of quantum sensing devices with a clear military application include radar, magnetometers, and gravimeters.
The stealthy navigation of underwater vehicles is a very challenging problem. Indeed, radio-frequencies and GPS signals are generally unable to penetrate water. Similarly, astronomical navigation using the position of the stars typically requires the vehicle to travel close to the surface of the sea, increasing the risk of detection. Also, acoustic sounding for navigation using bathymetry maps would reveal the position of the vehicle.
Therefore, current underwater navigation systems usually depend on sophisticated inertial navigation systems. These navigational tools mainly consist of accelerometers and gyroscopes to measure the motion and rotation of the vehicle. This information is constantly updated and used to calculate the best estimate of the current position, orientation, and velocity of the vehicle using dead reckoning techniques. Dead reckoning techniques are used to estimate the current position of a vehicle by using a known value of a previous position (known as a fix), and advancing the vehicle according to its measured velocity and plotted course.
The problem of underwater navigation is compounded if the vehicle is located in high latitudes; e.g., near the North Pole. In this situation, gyroscopes and compasses become unreliable and lead to big errors in the dead reckoning estimations made by the inertial navigation system. Indeed, the Arctic region contains the geomagnetic North Pole and Earth's rotation axis, which are the singular points for the operation of magnetic compasses and gyrocompasses, respectively.
Further challenges emerge if the vehicle is traveling under the Arctic ice shelf. The draft of the ice canopy varies from 0 to 100 feet, while the submerged portions of icebergs may extend many hundred feet under the sea. Also, it is known that the thickness and topography of the sea-ice canopy is highly variable throughout the year. Indeed, temperature variations and the effect of surface winds and underwater currents can drastically change the structure of the ice canopy. As a consequence, any possible ice canopy topographic maps may become obsolete very quickly.
Gravimeters and gravimetric maps can be used along the inertial navigation system. Gravimeters can be used along terrain and gravimetric maps to identify the current position of the vehicle, or as a real-time terrain estimation tool. Even though gravimetric terrain estimation systems are stealthy, current technology may not be able to fully resolve the ice canopy. Indeed, while the average density of typical sedimentary rocks (e.g. soil gravel, clay, sand) is of about the double of the density of water, ice density is about 90% of the density of water. In other words, the gravitational signature of sea ice is much weaker than the one from typical constituents of the ocean floor. However, quantum gravimeters could offer the possibility of highly sensitive sensors able to resolve the topography of the ice canopy.
In general, Arctic ice has the same strength as poor-grade concrete. Nonetheless, an accidental collision with the ice canopy could severely damage an underwater vehicle. To avoid collisions with the ice canopy, Arctic underwater vehicles use an active sonar array with acoustic sonar projections pointing towards the front, top and the bottom of the vehicle. This active sonar array system is shown in FIG. 1. These sensors provide information about how close the vehicle is with respect to the ice canopy and the ocean floor.
Unfortunately, in the case of Arctic military operations, active sonar will give away the position of the underwater vehicle. In addition, as shown in FIG. 2, the underwater vehicle has to navigate in the presence of a wide variety of natural and man-made obstacles.
Furthermore, a static target (zero Doppler) close to the ice canopy will be nearly invisible to most active and passive sensors. In other words, navigation close to the ice canopy offers tactical superiority. As such, underwater Arctic vehicles need to be highly maneuverable and able to ascend rapidly towards the ice canopy. To this end, the underwater vehicle generally requires having a very good estimation of the ice canopy topography. But then again, even though traditional sonar arrays are very efficient to elucidate the shape of the ice canopy, their strong acoustic signals give away the position of the underwater vehicle. Therefore, it is necessary to develop a stealthy system to aid in the highly maneuverable navigation of underwater Arctic vehicles.